Ghostscript is just that, a GHOSTscript. Frankly, you can install it and forget it's there because if you are using it for programs like FreePDF, you don't have to do any configuring to make it work. FreePDF checks to make sure it's installed, and takes care of the rest. Gostscript is an "interpreter for the PostScript language and for PDF." Need more info? Check out the Project Page above.
Screenshots:
If you run Ghostscript, you'll just see a command line screen which is useless to laymen like myself. For the reasons I need it, I'll never have to run this as a stand alone program:
